Producing chemicals from waste has two major positive environmental impacts: on the one hand it is a means of treating a residue, on the other hand it displaces the use of fossil fuels (or other non renewable raw materials) for the production of those chemicals. To date, the attempts to produce resources from waste have focused on the production of energy or biogas and only recently there has been interest on producing medium-high value chemicals. Mixed-culture fermentations are potential candidates to make the biosynthesis of chemicals economically attractive with respect to the chemical counterpart. In effect, in contrast with pure-culture processes, mixed-culture fermentations do not require sterile conditions and can easily operate in continuous. However, the behaviour of mixed-culture populations at new conditions is difficult to predict, making the development of a new process a formidable challenge. The main objective of BIOCHEM is to provide an integral method for design of mixed-culture fermentation with the aim of producing higher-value chemicals.BIOCHEM relies on mathematical models to optimise the new process on two key aspects: ensure that the mixed-culture population produces the desired product and increase the rate of production As a demonstration, we will develop in BIOCHEM a process for the viable production of volatile fatty acids (VFA), i.e. acetic, propionic, butyric and valeric acids from low grade biomass (food wastes) by anaerobi (co-)fermentation. The selected case study is especially interesting. Acetic acid global demand is approximately 10.3 million tonnes with wide applications in paints, adhesives, protective coatings and polymers. Propionic, butyric and valeric acid are produced in smaller quantities but have a higher added value and are used in animal feed and food preservation. These VFAs can also be used as building blocks of longer chain organic acids, aldehydes and alcohols with a wider application range.